This is according to a post on Reddit in which the original poster claims to have received an email from Amazon Germany informing him that the game’s release had been pegged for the 9th of March. It is possible that the date given by Amazon Germany might have simply been a placeholder, but it does seem like a very specific date for a placeholder.
As pointed out by some in the thread, placeholder dates are usually set for the end of the month, so to have a very specific date like the 9th of March suggests that it could be the real deal. That and the fact that this is Amazon who probably is privy to information the rest of us don’t, there is a good chance it could be real.
As to why it was delayed, the folks at Naughty Dog had previously stated, “It’s become clear to us that this game is much more ambitious than we originally envisioned. So we’ve made the difficult choice of pushing the game’s release date.” In any case since this is not an official announcement, we suggest you not get your hopes up just yet.